The use of carbon nanotubes for many practical applications often requires a precision landing of individual nanotubes into various functional structures and devices. In this regard, the synthesis of aligned and/or micropatterned carbon nanotubes has played a critical role in facilitating the integration of carbon nanotubes into certain useful devices (e.g. electron-emitters, transistors etc.). However, a more general self-assembling approach would allow the construction of individual nanotubes into various functional structures with a molecular precision. For this purpose, the site-selective chemical modification of carbon nanotubes is essential. Recently, judicious application of site-selective reactions to non-aligned and aligned carbon nanotubes for selectively modifying nanotube tips, inner and/or outer walls has opened a rich field of carbon nanotube chemistry. It has been demonstrated that the sidewalls of carbon nanotubes are rather unreactive due to the seamless arrangement of hexagon rings without any dangling bonds, and that the fullerene-like tips of carbon nanotubes are more reactive than the sidewalls for chemical attaching with various chemical reagents. However, the asymmetric functionalization of carbon nanotubes with each of their two end-tips attached by different chemical reagents remains a challenge. The asymmetric end-functionalization, if realized, should significantly advance the self-assembling of carbon nanotubes into many new functional structures with a molecular-level control.
Therefore, there is a need for asymmetric functionalized carbon nanotubes, and for methods of preparing them.